This invention relates generally to apparatus for determining the spatial location of an object and more particularly to apparatus for determining the position of an underwater body relative to a support platform on or above the sea surface.
When operating an underwater body from an overhead support platform, such as an aircraft, it is often necessary to accurately and continuously measure the relative position of the body with respect to the support platform. Present known methods for accomplishing this type of position determination comprise methods including acoustic tracking and calculation techniques. Acoustic tracking typically utilizes an acoustic beacon or transponder normally mounted on the body to be located with a directional receiver located on the tracking support platform. While such apparatus can provide accurate measurements, it requires the support platform to insert a receiving array into the water and is thus limited to relatively low speeds of advance through the water due to the flow noise induced by or in the receiving hydrophone array. This often presents a substantial problem when the support platform is a high speed craft such as an aircraft or air cushion vehicle.
Calculation of the position of an underwater body in such an arrangement also involves measuring tow cable parameters such as length, exit angle from the tow craft, and tow tension or body depth below the surface. Errors in body position due to water currents cannot be accounted for and the method is limited to towed bodies as opposed to tethered and autonomous undersea craft. A variant of the method of calculation also involves the calculation of a dead reckoning position using various sensors in conjunction with an inertial platform. Such equipment is relatively expensive and requires periodic calibration from an external position source to compensate for accumulated errors.
Accordingly, it is an object of the present invention to provide an improvement in the method and apparatus for determining the position of a body relative to a support platform.
It is another object of the invention to provide an improvement in method and apparatus for determining the position of an underwater body relative to a tracking craft on or above the water surface.
It is yet a further object of the invention to provide a method and apparatus for determining the relative position of an underwater body relative to an aircraft through the use of a beam of laser energy.